Chad Greenway was encouraged by the effort of the first unit defense in Friday’s 36-14 preseason win over Buffalo. On two first-quarter possessions, the Vikings allowed only 11 yards and one first down, getting off the field quickly both times. But just as it was premature to panic after the Vikings allowed 260 rushing yards in a preseason loss in San Francisco a week earlier, Greenway wasn’t about to assert that the Vikings’ defense is now suddenly in top form.

“You take it with a grain of salt,” he said. “Obviously it’s not a full game and you’re not going to see all of their best looks. And we didn’t put our best stuff at them either. So it’s a snippet of where we’re at, nothing more than that. I don’t think we take too much out of that game other than that it was definitely a step in the right direction.”

Smith, Raymond now the starters at safety

The Vikings are almost certain to start rookie Harrison Smith and second-year defensive back Mistral Raymond together at safety against the Chargers. Raymond played well in Friday night’s win over Buffalo and has earned the right to assume more responsibility over Jamarca Sanford until further notice.

So get ready for the Smith-Raymond pair to be more permanent.

“We want to look at that tandem again and see how they progress,” Frazier said. “We’ll still work Jamarca in there. But as we speak we’ll want to go with those two to begin.”

Injury update

Among the notable absences from Sunday’s practice: tight ends John Carlson and Kyle Rudolph and cornerback Chris Cook. Carlson is still not ready to return to practice as he continues nursing a knee sprain that he suffered in practice July 31.

Rudolph and Cook both suffered blows to the head in Friday’s game against Buffalo and are currently being evaluated for concussion-like symptoms.

In other injury news, nose tackle Letroy Guion, who suffered a knee injury in an Aug. 10 loss at San Francisco, is making good progress and should be ready to play again this week against the Chargers. Same goes for safety Robert Blanton (hamstring), running back Jordan Todman (ankle) and offensive tackle DeMarcus Love (pectoral).